I know you said you are anti-cannula, but I've used the Aqua Lung PHODS for work similar to what you say you'll be in, up to 15,000ft, with no issues. The altitude based auto-start/stop and automatic O2 regulation is awesome. It's minimalistic compared to a mask, never interfered with shooting with a DSLR, and is a tiny overall package (and not hard mounted at all).
Mike